As is more fully set forth in above-mentioned application Ser. No. 136,441, nematic-phase liquid crystal layers sandwiched between opposing parallel transparent plates rubbed unidirectionally with transparent conducting films on those surfaces contacting the liquid crystal layer provide a unit whose optic axis lies in the direction of the unidirectional rubbing. If the directions of rubbing are at an angle with respect to each other, such as 90.degree., the effect has been found to be an optical media which rotates the plane of polarization by the angular difference between the directions of rubbing. It has also been found that, if an electric or magnetic field of predetermined magnitude is applied across opposing sections of selected films, the rotation of polarization is terminated.
According to the concept of application Ser. No. 136,441, the application of the field across selected conducting film areas can be used to establish a plurality of selectively operable light shutters by disposing the liquid crystal unit between parallel or crossed-polarizers. While many modes of operation are possible, the emphasis herein will relate to the control of displays where there is a plurality of character, image or digit positions and where, in each position, there is a plurality of segments which must be selected by respective signals, preferably electric potentials, to define a character, image or digit. For simplicity, the invention will be discussed with respect to a display for decimal digits, where each digit selection includes seven film segments referenced, respectively, as segments A, B, C, D, E, F and G. In a four-decimal digit display, there are four sets of the digit defining segments. Four sets of the digit defining segments are on the inner surface of one of the opposing plates containing the liquid crystal and, on the inner surface of the other plate, there are four distinct digit position selecting films each arranged to align with a corresponding one of the four sets of digit defining segments. It will be understood that any number of digit segment sets may be used and that many variations in character or image configurations may be controlled.
The problems arising in controlling a multidigit display of the type mentioned above is that the total number of control signals, prior to the present invention, has been the product of the number of digit positions times the number of digit characterizing segments or dots in each position. This has been solved, in the prior art, by introducing memory elements such as flip-flops or storage capacitors to hold the digit or character configuration for each digit position or other complicated electrical means to permit the multiplexed scanning of a plurality of positions by means of a single control where only the segment selections of a single character are presented at one time. Basically, the problem has been to simplify the control from a complex parallel control where all digits or characters had to be presented simultaneously to a simplified control where the character positions can be scanned to reestablish the proper display for that position alone.